1. Field of the Invention
The present invention relates to a method and apparatus for treatment of human or animal cell samples. In particular, the invention relates to treatment of the samples to enable diagnosis of clinical conditions. A sample is fixed on a flat surface such as a microscope slide and chemically treated with liquid for the purpose of sample hydration or dehydration, or sample staining, or in chemical analysis such as detection of antigens or nucleic acid sequences, for example. The liquids used to treat such sample include:
1. Organic solvents. PA0 2. Antibodies. PA0 3. DNA and RNA probes. PA0 4. Chemical solutions. PA0 5. Washing solutions.
2. Description of the Related Art
Conventionally the chemical treatment and the chemical analysis of the samples is done by immersing the glass slides on which the samples are fixed into beakers that contain the treatment solutions. Certain solutions are expensive and they are dispensed onto a slide using a pipette with the slide in a horizontal orientation and a glass coverslip is placed on top of the slide to provide spread of the solution and to slow evaporation. The conventional process is labour intensive, exposes workers to reagent fumes and possibly to contact with the chemicals. Accurate timing of the processing steps can also be difficult to achieve. The amount of liquid waste generated is often large, which may be a problem, since the waste that needs to be disposed can contain aggressive solvents or biohazards such as infectious viruses. To overcome these problems a number of inventions have been proposed for automating the process.
In U.S. Pat. Nos. 4,731,335 and 4,777,020 and 5,002,736 Brigati, D. et al there is described a system where two flat surfaces such as microscope slides are placed face to face with sample sides facing inward. Abutting coating portions of the slides define a capillary gap between the samples. This slide pair can be placed so that the lower edge of the slide pair connects with the treating liquid which will then migrate into the capillary gap. Liquid can then be removed from the gap by placing the slide pair on top of and in contact with absorbent material which will drain and absorb the liquid.
Shandon Scientific Limited U.S. Pat. No. 4,985,206 describes an apparatus for processing tissue. The core of the invention is a channel-defining element. This element is joined together with a slide holding the sample with the sample side facing towards the element. The element forms a channel between its main wall and the slide. When the channel is substantially vertical the upper part of the element forms a liquid dispensing reservoir. An operator or a liquid handling robot can then fill the reservoir with appropriate reagent. Gravity and capillary action will cause the reagent to migrate into the channel. Once the channel is filled with liquid and the reservoir is empty, the liquid will stay in the gap due to surface tension of the liquid. The liquid in the gap can be replaced by placing new reagent in the reservoir.
Toya, M. et al in U.S. Pat. No. 5,068,091 and UK patent 2,265,981 describes a substantially horizontal wedge shaped capillary gap between a microscopic slide and lower plateau. Liquids can be dispensed to an exposed end of the plateau and capillary action will cause them to migrate to the wedge shaped gap. The gap can then be cleared of the reagent by using suction. Surface tension of the liquid will keep the liquid volume together during the removal process.
The aforementioned prior art apparatus all suffer a disadvantage in that they can in some instances fail to provide an even treatment of the sample with the treating liquid. This is caused by air becoming trapped in the capillary gap. In the case of the Brigati inventions, capillary forces can only lift the liquid a certain distance upwardly from the lower edge of the slide pair and this can lead to a reduced treatment area on the slide. The speed of liquid removal cannot be controlled in the Brigati inventions. The capillary gap also needs to be drained before a new liquid can be applied. These form a disadvantage, because in certain cases it is desirable that the samples are not exposed to air at all when replacing liquids. This is desirable especially when using volatile liquids such as organic solvents that evaporate easily and may let samples dry out during liquid replacement. Sample drying can lead to reduced processing quality such as high non-specific staining. In other cases a film of liquid should be left on the sample to keep it moist during liquid replacement. In the remaining cases it is desirable that the samples are dried completely before applying a new liquid to ensure maximum concentration of the applied liquid.
The apparatus of Shandon has the additional problem that no provision is made for clearing the gap (filling it with air) between different liquid treatments and therefore any air voids trapped in the gap are likely to remain through the process. Also the apparatus of Shandon cannot provide capability to expose the sample to air during processing while liquids are replaced. In the apparatus of Toya M. et al the suction to clear the capillary gap can lead to a breaking-up of the liquid into two or more sections with only one section being sucked into the waste containment system and such an incomplete clearing of the liquid can cause unacceptable treatment of the sample.